1. Field of the Invention
The present invention relates to electronic bus switches used for transferring electrical signals from one location to another, and more particularly to the configurations or groupings of such bus switches.
2. Background Information
Bus switches have been used to isolate circuits from each other for many years. These switches provide a low on resistance that allows signals to transfer between sending and receiving circuitry and a high off impedance that isolates that circuitry from each other. The development of transistor technology, especially MOS transistors, has resulted in low-cost, very reliable semiconductor switches that are typically implemented as single pole single throw switches.
Isolating bus signals and thereby preserving bus signal integrity is a requirement of a modern system. When buses are shared, the signals traveling on the bus must not affect and must not be affected by circuitry and other signals not on the bus—bus isolation is required for proper system operation. This bus isolation is especially important when “hot swapping” is a feature of the system. “Hot swapping” is the ability to remove and insert circuit boards without removing power and without interrupting the system operations or damaging the system. Effective bus isolation is an ingredient meant to accommodate such “hot swapping.” Isolating circuits from one another is important across edge, socket or other types of connectors where the circuitry is at risk when connections or contacts are being made or broken. Plugging in the wrong circuit, miss-alignments, power spikes, and physically damaging the connectors and/or the contacts illustrate some of the problems when physically making and breaking connections.
In the past, mechanical relays and bipolar transistors switches were used, but for most applications, including transferring compatible analog signals, and virtually all digital computer circuitry applications, MOS field effect transistors (usually NMOS) are the bus switch component of choice. NMOS transistors provide low on resistances, can withstand the voltage/current stresses typically associated with digital electronics, are compatible with both high (5V) and low (3.3V) TTL logic signals, exhibit no “bounce” as found in some mechanical relays, include no “offset” drops (pn junction), exhibit minimal propagation delays, are reliable and can be densely packaged in the newest high pin out packages.
NMOS transistor switches are found in a wide variety of products, including desktop and notebook computers, hand held personal data assistants, servers, video/sound cards, mobile phones, video games, and communication electronics. These switches may also be used in multiplexers, switch based gates, and analog switches. In any event, bus switches may be found wherever electronics exist.
However, with the many applications for bus switches, there is a wide variety of organizations, bit widths, pin outs, and package sizes available from many manufacturers. Moreover, circuit design revisions often dictate different configurations and/or organizations of the bus switches that may require different packages and/or control logic. A sampling of applications includes bus bit widths of four, five, eight, ten, sixteen, twenty, forty and eighty bits, available in many different packages. However, any bit widths can be accommodated limited only by the current packaging or interconnecting technology and the different configurabilities required by the system designer.
At the present time, manufacturers using and specifying bus switches must stock many different device types, and they must retain older types for rework and repair. The present invention is directed to resolving these limitations.